Polymorphisms in the tumour necrosis factor gene are not associated with severity of inflammatory polyarthritis

BACKGROUND

Tumour necrosis factor alpha (TNFalpha) is a powerful inflammatory mediator in rheumatoid and other types of inflammatory arthritis. Polymorphisms within the TNFalpha gene have previously been investigated to determine their role in the aetiopathogenesis of rheumatoid arthritis (RA), but it is unclear whether reported associations are with susceptibility to, or severity of, disease.

OBJECTIVE

To examine the association between both individual TNFalpha single nucleotide polymorphisms (SNPs) and haplotypes with the development and severity of erosions by 5 years in patients with inflammatory polyarthritis (IP).

METHODS

438 patients from the Norfolk Arthritis Register observational inception cohort of patients with IP were x rayed 5 years after disease onset. They were genotyped for nine SNPs mapping to the TNFalpha gene, using a SNaPshot primer extension assay. Haplotypes were constructed in patients with IP, who were compared for the presence and extent of erosions at 5 years.

RESULTS

No association between individual TNFalpha SNPs or haplotypes in the patients who developed erosions at 5 years compared with those who remained non-erosive was found. Restricting analysis to patients who satisfied ACR criteria for RA by 5 years did not affect the conclusions.

CONCLUSION

The TNFalpha gene does not seem to be associated with severity as assessed by erosive outcome at 5 years in patients with IP.

High resolution linkage and association mapping identifies a novel rheumatoid arthritis susceptibility locus homologous to one linked to two rat models of inflammatory arthritis

Rheumatoid arthritis (RA) is an oligogenic autoimmune disease but, to date, linkage and association to major histocompatibility complex (MHC) has been the only consistent finding in genetic studies. However, MHC is estimated to contribute only 30-40% of the total genetic component to disease susceptibility. Studies in animal models of inflammatory arthritis have identified a number of putative vulnerability loci but the homologous regions in the human genome have not previously been investigated as candidate RA susceptibility loci. We have investigated linkage to five regions homologous to those identified in animal models of inflammatory arthritis in RA affected sibling pair (ASP) families. Linkage to 17q22 syntenic to a susceptibility locus common to two experimental rat models was detected in 200 RA ASP families and replicated in a further 100 RA ASP families. Linkage to additional markers mapping to the area has refined the extent of linkage to a 4 cM region. Association to one of the markers (D17S807) was demonstrated in this cohort using extensions of the transmission disequilibrium test. Association to two 2-marker haplotypes including this marker was detected in an independent cohort of single-case RA families, thus narrowing the region harbouring the aetiological mutation to approximately 1 cM. This is the first time that an arthritis susceptibility locus mapped in experimental animal models of disease has been used to identify a novel RA susceptibility locus in humans. The difficult task of identifying a disease mutation from a linkage result should, in this case at least, be facilitated by the combined use of animal and human based investigations.

Cloning, expression, and physical mapping of the 3beta-hydroxysteroid dehydrogenase gene cluster (HSD3BP1-HSD3BP5) in human

Seven members of the human 3beta-hydroxysteroid dehydrogenase (3beta-HSD) gene family (HGMW-approved symbols HSD3BP1-HSD3BP5) have been cloned and physically mapped. HSD3B1 and 2 express 3beta-HSD enzymes; HSD3Bpsi1-5 are unprocessed pseudogenes that are closely related to HSD3B1 and 2 but contain no corresponding open reading frames. mRNA is expressed from psi4 and psi5 in several tissues, but with altered splice sites that disrupt reading frames. A 0.5-Mb contig of 3 yeast artificial chromosome and 32 bacterial artificial chromosome genomic clones contained no additional members of the gene family. The seven genes and pseudogenes mapped within 230 kb in the order HSD3Bpsi5-psi4-psi3-HSD3B1-psi1-psi2 -HSD3B2. HSD3B1 and 2 are in direct repeat, 100 kb apart. Six HSD3B2 mutations involve substitutions that are present in several of the pseudogenes. In four cases, mutations arose in CpG sites that are conserved within the gene cluster. The tendency for CpG sites to mutate by transition provides an adequate explanation for these HSD3B2 mutations, which are unlikely to be due to recombination or conversion within the gene family.

Generation of a contig comprising YACs and BACs within chromosome region 1p13.1

Chromosome region 1p13 is known to show loss of heterozygosity (LOH) in a number of human tumor types, including breast. We have generated a contig comprising YACs and BACs spanning part of 1p13.1 which includes the smallest region of overlapping loss identified in our earlier studies. The contig is anchored to the genetic map by a number of microsatellite markers, and by the use of CEPH YACs. We have excluded a number of candidate genes from this region, and we have oriented the contig with respect to the centromere and a number of other genes and markers on 1p13. This resource will be valuable in mapping the target for LOH in breast and other tumors, and may also be useful for the genetic analysis of other genes or diseases known to map to this region.

Identification and cloning in yeast artificial chromosomes of a region of elevated loss of heterozygosity on chromosome 1p31.1 in human breast cancer

We have mapped a region of high loss of heterozygosity in breast cancer to a 2-cM interval between the loci D1S430 and D1S465 on chromosome 1p31.1. This region shows allelic imbalance in around 60% of breast tumors. As part of a strategy to clone the target gene(s) within this interval, we have generated a yeast artificial chromosome contig spanning over 7 Mb. YACs from the CEPH and Zeneca (formerly ICI) libraries have been obtained by screening with PCR-based STSs from the region for both previously identified loci and newly isolated STSs. The YACs have been assembled into a contig by a combination of approaches, including analysis of their STS content, generation of new STSs from the ends of key YACs, and long-range restriction mapping. These YAC clones provide the basis for complete characterization of the region of high loss in breast cancer and for the ultimate identification of the target gene(s).

Establishment of the marker order pter-NRAS-NGFB-D1S189-D1S252-D1S440-D1S453-D1S514-CEN-D1S442-D1S498-qte r in relation to the centromere on human chromosome 1

Recent developments in genetic linkage mapping of the human genome have generated a large number of short tandem repeat polymorphic markers (Weissenbach et al. 1992, Gyapay et al. 1994), and eventual integration of these markers into a physical map is a logical progression. A number of Généthon microsatellite (CA repeat) markers have been provisionally localized to 1p13, but their exact position with respect to other sequences is unknown. In order to confirm the order of these markers and their position with respect to known genes within 1p13 and the centromere, we have isolated yeast artificial chromosomes (YACs) corresponding to the markers and have carried out double and triple fluorescence in situ hybridization (FISH) studies. Knowledge of both the order of microsatellite markers and their integration with a physical map of known genes can be an essential component in analysis of disease loci such as human cancer, where regions of chromosomes showing high levels of loss of heterozygosity need to be mapped in detail.

Allelic imbalance on chromosome 1 in human breast cancer. II. Microsatellite repeat analysis

We have determined regions of allelic imbalance in human breast cancer cells using highly polymorphic microsatellite markers, which can be rapidly typed by the polymerase chain reaction (PCR) using very small amounts of DNA. It appears that there are several regions of chromosome I which may be the targets of allelic imbalance, including some regions which have been identified previously by different groups. The detail with which we have mapped these regions of imbalance is, however, much greater than has been previously reported, and we have been able to localise these regions to small intervals of the genome. In addition we have identified previously uncharacterised regions of allelic imbalance on chromosome arm 1p, one of which (at 1p22-31) is lost in a high proportion of malignant lesions. We are currently attempting to analyse this latter region in detail in order to identify and characterise the sequence(s) involved. Study of such regions should help us understand some of the mechanisms underlying the development and progression of breast cancer.